Malleable iron process



Patented June 17, 1941 'MALLEABLE moN'rRocEss .Harry A. Schwartz, Cleveland Heights, Ohio, assignor to NationalMalleable and Steel Castings Company, Cleveland, Ohio, a corporation of Ohio No Drawing.

This invention relates to a process for reduc--' ing the annealing time of white cast iron when converting it to malleable iron and in improving the physical properties of the resulting malleable iron. More particularly the invention concerns the improvement of said physical properties and annealing time by a reduction 'of the moisture in the air blast used in the melting furnace.

It has been observed on dilferent occasions that the physical properties of malleable iron varied considerably even when made by the same proc ess and when the usual analysis showed no substantial difference in the generally accepted variables. During an investigation into the cause of this behavior of the metal I discovered that the hydrogen inthe white cast iron,- although present in minute quantities, varied in some specimens by several hundred percent over that in other specimens. Correlation of the hydrogen in a series of specimens with the physical properties referred to, a cupola, air furnace, rotary melting furnace, commercially known as the Brackelsberg furnace, or any other device in which'the products of combustion come in contact with the molten white cast iron may be understood. The process is equally operable in any of these methods and I have no desire to restrict myself to the use of any particular form of melting equipment. Moreover, it is operative in cases where two furnaces are used in conjunction with each'other, as where the metal is melted in a cupola and further refinement thereof takes place either in an air-furnace or in an electric furnace.

The improvement made in the physical properties of malleable iron, which is the product of the white cast iron above referred to, by alter- TABLE; I i

- Q assaga e Percent- 1.12 52216 16.0 0.00046 .04 52834 14.0 0.00052- .02 51,987. 6.6 0.00050 .86 46151 1.0 0.00064 .01 45998 6.5 0. 00000 1.10 51532 7.5 0.00060 I .06 44121 as 0.00058' Average 2.61 .91 44352 16 0.00066 For specimens 1; 2 and 3 the table indicates: that the average tensile. strength is 52,346 pounds per square inch and the average percent elongation 15.5 for the malleable iron made from the .white iron. Theaverage hydrogen content is 0.00049 percent. In specimens 4, 5, 6 and 7 the. average hydrogen content is shown as 0.00066 percent. It will be observed that the averagereduction in tensile strength for these last four specimens is about 15.0 percent and that'the percentage of elongation has been cut approximately in half. I I

.The effect of hydrogen content in white cast iron upon the rate of formation of graphite in the subsequent annealing process can be observed by reference to Table II.

TABLE II Group-1 Graphite Hydrogen sp cime gg gan o Percent Percent 2 0.00020 0.00 0 0.00025 0.54- 10 0.00030 0.42 11 0.00030 0.40 12 0.00040 0.38

Average 0.00030 0.430

ing the hydrogen content will be understood by I reference to Table I below:

Application February 15, 1040. Serial,No.319,105

6 Claims. (01. 148-:3)

TABLE II Group 2 Hydrogen Specimen hours at weight Q) Percent Percent ew test? Specimen by hours at weight Percent Percent In order to emphasize the difference in result between high and low-values of hydrogen Table II is divided into three groups. In Group 1, wherein all values of hydrogen are under 0.00050 per- 7 cent, the amount of graphite deposited in four hours is uniformly good. In Group 2, with hydrogen between 0.00050 percent and 0.00060 percent. the deposition of graphite is very erratic. In Group 3, which shows hydrogen over 0.00060 percent, the amount of graphite deposited is uniformly low. This suggests that when the hydrogen in white cast iron is much above 0.00050 percent a much longer time for anneal can be expected.

The above tables clearly indicate that very small amounts of hydrogen are definitely detrimental to the strength of the resulting malleable iron and to its annealing rate. One source of hydrogen in white cast iron is the moisture in the air blast. Hydrogen may also be present due to the use of rusty scrap, moisture on the fuel or melting stock, or to the hydrogen in the melting stock itself. The effect of moisture in the air blast on the hydrogen content of the white iron is'illustrated in Table III.

TABLE III Moisture Percent Moisture Percent Difl'crgrains hydrograins hydro ence in per gen by per gen by hydrocu. ft. weight cu. ft weight gen cupola l. 0. (D024 2. 01 0. 00083' 0. 00050 All l. 30 0. 00035 2. 61 0. 00091 0. 00056 Bmckelsberg.- 1. 30 0. 00052 1. 85 0. 00089 0. 00037 used with the furnace has a great effect on the amount of hydrogen present. An increase in moisture from 1.30 to 2.61 grains per cubic foot increases the hydrogen in the cupola from 0.00024 percent to 0.00083 percent and in the air furnace from 0.00035 percent to 0.00091 percent. In the Braokelsberg furnace an increase in moisture from 1.30 to 1.85 grains per cubic foot raised the hydrogen from 0.00052 percent to 0.00089 percent.

That the moisture of the air blast is not the only source of hydrogen is indicated by the fact that metal produced by cupola-electric furnace duplexing on a rather damp summer day but from extremely rusty scrap contained 0.00115 percent hydrogen, whereas iron produced from ordinary scrap under the same conditions contained 0.00083 percent. 1

From Table III moisture contents that would result in about 0.0005 percent hydrogen for the different types of melting furnaces may be readily calculated by linear interpolation. Interpolating in this manner to obtain the moisture content of the air blast for the cupola and air furnace that would result in a hydrogen concentration of not over 0.0005 percent, the figure for the cupola is approximately 1.87 grains per cubic foot and for the air furnace 1.65. Although reasoning based on the mass law andvarious as sumptions as to melting conditions might lead to more complicated methods for interpolating, I feel that for practical purposes such a course is scarcely justified over mere linear interpolation.

It is to be expected that the hydrogen concentration will rise or fall so as to approach equilibrium with the flame of the furnace even though complete equilibrium will not be attained in a commercial process. The limiting moisture content in the air to attain a given desired hydrogen content in the iron is thus to some degree dependent on the hydrogen content of the charge. Since, however. according to my invention the desire is to minimize the hydrogen as far as possible, no harm will result if the blast is dried as far as is commercially feasible.

From what has been said above, it will be clear thatany step that will reduce the amount of hydrogen in the white cast iron will improve the physical properties of the resulting malleable iron and also reduce the annealing time for producing the latter. Moreover, any step that will lower the moisture content of the air blast used in melting furnace is of advantage in making malleable iron. The moisture content of the air may be reduced either by refrigeration or by absorption of water by suitable substances such as silica gel or calcium chloride.

In practising my invention I follow the usual procedure for making white iron for conversion into malleable -iron with the addition that the moisture content of the air blast supplied to the furnace is reduced by suitable drying means so 'as to control the hydrogen in the metal.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention in the use of such terms of excluding any equivalents of the matter described but recognize that various modifications are possible within the scope of the invention.

I claim:

1. A process for improving the physical properties and for shortening the annealing time, of malleable iron which comprises melting the iron ations in the moisture content of the air blast in fuel fired furnace and maintaining the drogen in the melted iron under about 0.0005 percent by controlling the moisture content of the air blast used to support combustion of the fuel.

2 That improvement in the art of making malleable iron which comprises melting the iron in a fuel fired furnace, maintaining the amount of hydrogen in the melted iron below about 0.0005 percent, pouring the metal into molds and annealing the resulting article.

3. A process for improving the physical properties andfor shortening the annealing time of malleable iron which comprises melting the iron in a fuel fired furnace and maintaining the moisture content of the air supplied to the fuel under about 1.65 grains per cubic foot to control the hydrogen content of the iron.

4. A process for making malleable iron com prising melting the usual ingredients for white iron in a fuel fired furnace, maintaining the hydrogen content of the melt below about 0.0005

percent to improve the physical properties theremaintaining the moisture content of the air supplied to the fuel under about 1.30 grains per cubic foot to control the hydrogen content of the iron.

HARRY A. SCHWARTZ. 

